This invention relates to a filter using a charge transfer device, and more specifically to a filter that can be effectively employed in a system for processing color television signals.
Along with the rapid progress of semiconductor integrated circuit techniques in recent years, charge transfer devices have been developed.
It is known that the charge transfer devices can be broadly divided into charge coupled devices (CCD) and bucket-brigade devices (BBD). The CCD is more advantageous for applications in the video frequency or to a signal having a 10 MHz sampling frequency.
On the other hand, developments in semiconductor technology have resulted in a higher degree of integration, a higher operation speed of digital memories and in reducing the cost of production. Digital signal processing techniques have become widespread in a number of electro-communication fields. Remarkable improvements have been made in digital processing techniques in video signal processing, and fully digitallized devices have been practically used in frame synchronizers, time base correctors, and the like. However, these techniques have an essential need for analog and digital conversion systems at their input/output portions and conversion systems are not yet economical at present. In other words, though digital signal processing techniques make it possible to secure accuracy by increasing the number of bits, it calls for large power consumption, becomes large in size and is likely to become very expensive.
This tendency becomes all the more pronounced as the frequency becomes higher, and it seems unlikely that the digital techniques could be applied to home-use appliances processing a video frequency signal. Since signal processing using the CCD does not have a large power consumption, is small in size, and inexpensive, it is well suited for electro-communication, especially for appliances in the video frequency. The signal processing in these appliances is accomplished by a comb filter. As to a signal processing circuit using a comb filter of the CCD, a chrominance-luminance separation circuit is disclosed in the specification of U.S. Pat. No. 4,096,516.
The comb filter used in the abovementioned chrominance-luminance separation circuit includes a first CCD delay line for delaying an input signal by at least one horizontal scanning period, a second CCD delay line for delaying an input signal to produce an output signal which is faster by one horizontal scanning period than the output signal of the first CCD delay line, a third CCD delay line for first inventing an input signal and then delaying the signal to produce an output signal which is faster by one horizontal scanning period than the output of the first CCD delay line, a first adder for adding the output of the first CCD delay line to that of the second CCD delay line to obtain a first output, and a second adder for adding the output of the second CCD delay line to that of the third CCD delay line to obtain a second output, whereby a luminance signal is obtained as the first output and a chrominance signal as the second output.
However, the known comb filter is suited for the separation of chrominance-luminance signals of so-called NTSC color television signals, but is not so well suited for other applications. Besides the chrominance-luminance separation circuit, there are a large number of applications of the comb filter processing a video frequency signal such as in a contour compensation circuit in a color camera, a foldover distortion elimination circuit in sub-Nyquist sampling, an adjacent-channel interference elimination circuit in a home-use VTR, and so forth, and the types of the comb filter include a 1H type, a 2H type, and so forth. In order to cover these numerous applications, it is more advantageous to form a basic block using a CCD, to connect a plurality of the resulting basic blocks and to modify the connection thereof to obtain an intended construction. This method makes it possible to furnish a low-cost mass-produced CCD of a limited type, but with such versatility that is would be applicable to a variety of appliances.